For us, it depends upon how the overmold is applied. If the part is made in a two-shot mold, then we have just one drawing. If the first shot is molded separately and then inserted into the second shot mold, then we have two drawings.

Personally, I would try to solve the mystery first. I would like to know before I do the drawings how the part is going to be molded. One obvious reason is that two drawings are needed in one case and only one in the other. Also, the tolerances and even features required are different depending on how the part is molded. (You need tighter control over the size of the first shot tool if if is going to fit into another mold. You may need mechanical interlock features in an insert mold that might not be necessary in a two-shot mold as the first shot material is warmer and the second shot loses less heat to the mold. The gating may need to be different. There are a whole raft of differences in the tool construction that may affect how you design the parts.) If that decision can't be made yet, then I guess I would default to two drawings, since both will be needed if you go with insert molding.